The German patent publication 3,637,393 C, the German patent publication 3,811,399 A and the German patent publication 2,541,070 A disclose composting methods, in which organic materials, more particularly those containing waste materials (or "biowaste"), are composted. More particularly the said German patent publication 3,637,393 C, describes a method and an apparatus, in which organic materials are composted in a sealed container using forced ventilation.
In the prior art composting methods exhaust air purification takes place, with the production of water, since on falling below the dew point on cooler surfaces water vapor entrained in the air and originating from the biological reaction or, respectively, conversion is condensed out.
The composting of kitchen and garden waste, which has been separately handled in the garbage collection service, leads to the release of substantial quantities of water. When the hot exhaust air has cooled down so far that no odors escape into the atmosphere, condensate is produced. So far exhaust air from biological processes, more particularly from composting processes, has been passed through biological filters for reducing the odor fraction, the humidity water being substantially caused to precipitate, this meaning that the filters became clogged on the inlet side. The liquid then produced, which is hard to dispose (also named "percolating water") is heavily contaminated owing to the contact with the biomass and accordingly possessed a very high oxygen requirement (a CSB of approximately 40,000 to 80,000 mg O.sub.2 /l). As a consequence of technical developments filters were provided with upstream cooling traps or scrubbers so that the liquid no longer came into contact with the biomass, in order to reduce the CSB (chemical oxygen requirement) value and the BSB (biochemical oxygen requirement) value of the condensate. The CSB values then resulting amounted approximately to 5,000 mg O.sub.2 /l. This value as well is however still in need of improvement.